Compared with linear polymers, branched polymers have low melt viscosity and solution viscosity, good solubility and multi-end groups due to the unique three-dimensional spherical structure. Addition of branched polymers is recommended for modification of polymers to prepare coatings with high solid content, and their use as adhesives, polymer catalysts and for drug delivery. However, there are still challenges for promoting the application of branched polymers owing to the limitation of the quantities of branched polymers that can be synthesized with needed branched structure and behavior. Therefore, it is still necessary and important to develop and explore the synthesis methods of branched polymers.
At present, the main processes for preparing the branched polymers are (a) live/controlled free radical solution polymerization using the inimer or divinyl monomer and (b) conventional free radical polymerization in the presence of chain transfer monomers. However, the reaction conditions of live/controlled free radical solution polymerization are relatively harsh and polymerization of monomers and polymer structures is limited along with other disadvantages such as the obtaining of relatively low molecular weight branched polymers, whose molecular weight distribution is relatively wide. In contrast, the reaction conditions of conventional free radical polymerization using chain transfer monomer is simple, but the molecular weight of the obtained branched polymers is relatively low and their molecular weight distribution is relatively wide. These two main types of polymerization processes for the preparation of branched polymers also have two common drawbacks during processing, i.e., high monomer conversion requires longer time for polymerization, and the reaction process uses a large amount of organic solvent, which could be hazardous to the environment. These deficiencies have restricted the development of large-scale application of branched polymers to some extent. Emulsion polymerization uses water as the medium, which is better for environmental protection and safety. In addition, by using the redox initiator system, the polymerization could be done at or below room temperature owing to the low activation energy needed for the initiation of reaction. The advantages of the polymerization process using this redox initiator system are fast polymerization speed, i.e., short reaction time leading to high polymer molecular weight and narrow molecular weight distribution of the polymers. The development of simplified and facile synthesis methods for the preparation of branched polymers is an important direction in the study of branched polymers, which is of great significance not only to the theoretical study but also for large-scale application of branched polymers.